Sintered ultra hard material cutting elements such as tips for metal machining inserts, for example, typically include an ultra hard cutting layer bonded to a substrate, forming what is often referred to as a compact. The ultra hard cutting layer is generally formed by a high pressure, high temperature (HPHT) sintering process and the cutting layer is typically bonded to the substrate during the sintering process.
The ultra hard sintered compact is generally formed from particles of ultra hard material that are compacted and solidified during the sintering process. The ultra hard particles may be in powder form prior to sintering. Ultra hard particles used to form sintered compacts include diamond and cubic boron nitride, which form polycrystalline diamond (PCD) and polycrystalline cubic boron nitride (PCBN), respectively.
Sintered compacts are conventionally formed by placing ultra hard material particles within a refractory metal enclosure and sintering the enclosure and contents under HPHT conditions. A shortcoming associated with this conventional formation process is that the high-pressure, high temperature heating process and subsequent cooling process, produce an ultra hard material layer having a periphery that includes edge cracks, chips and fractures. These edge cracks, chips and fractures typically initiate at the enclosure and continue growing into to the compact ultra hard material layer. This cracking, chipping, fracturing, etc. renders the outer portion of the ultra hard material layer unusable. Fracturing, cracking, and chipping is especially prevalent when forming relatively large (more than 50 mm diameter) ultra hard material layers. To avoid sintered compacts being delivered to customers having peripheries that include the above-mentioned defects, a significant amount of the outer portions of the PCD or PCBN sintered compacts must be removed, therefore reducing the useable diameter of the sintered compacts. This results in higher raw material waste and costs, higher processing costs, and lower HPHT press capacity efficiency and utilization. For example, using conventional methods, a disk-shaped sintered compact formed to a diameter of 58 mm, may include edge fracturing and cracking that requires the formed sintered compact to have parts of the peripheral portion removed resulting in a useable diameter of only 50-52 mm or less. In particular, according to the prior art, most sintered compacts formed to a diameter of 58 millimeters, for example, are finished to a diameter less than 55 mm.
Accordingly, it would therefore be desirable to produce an ultra hard cutting layer in which the high quality, useable cutting area is maximized.